Sharif Digital Repository

The static Coulomb potential of Quantum Electrodynamics is calculated in the presence of a strong magnetic field by computing perturbatively the vacuum expectation value of the corresponding Wilson loop in the lowest Landau level (LLL) approximation. In the LLL, two different regimes of dynamical mass, md yn., can be distinguished. These two regimes are |q2 | ≪ m2 d yn. ≪ |eB| and m2 d yn. ≪ |q2 | ≪ |eB|, where q is the longitudinal components of the momentum relative to the external magnetic field B. As it turns out, the potential in the first regime, |q2 | ≪ m2 d yn. ≪ |eB|, has the general form of a modfied Coulomb potential V1(R, θ ) = −α R A1(α, θ ) −γ A2 R (α 2 ,θ ) + γ 2 A3 (α,θ ) ,... 

We determine the shear viscosity of a hot and dense Yukawa-Fermi gas, using the standard Green-Kubo relation, according to which the shear viscosity is given by the retarded correlator of the traceless part of the viscous energy-momentum tensor. We approximate this retarded correlator using a one-loop skeleton expansion, and express the bosonic and fermionic shear viscosities, ηb and ηf, in terms of bosonic and fermionic spectral widths, Γb and Γ±. Here, the subscripts ± correspond to normal and collective (plasmino) excitations of fermions. We study, in particular, the effect of these excitations on thermal properties of ηf[Γ±]. To do this, we determine first the dependence of Γb and Γ± on... 

The effect of an exponentially decaying magnetic field on the dynamics of Dirac fermions in 3+1 dimensions is explored. The spatially decaying magnetic field is assumed to be aligned in the third direction, and is defined by B(x)=B(x)e z, with B(x)=B 0e -ξx" B. Here, ξ is a dimensionless damping factor and " B=(eB0 -1 /2 is the magnetic length. As it turns out, the energy spectrum of fermions in this inhomogeneous magnetic field can be analytically determined using the Ritus method. Assuming the magnetic field to be strong, the chiral condensate and the local electric current correlation function are computed in the lowest Landau level (LLL) approximation and the results are compared with... 

The complete quasiparticle spectrum of a magnetized electromagnetic plasma is systematically explored at zero and nonzero temperatures. To this purpose, the general structure of the one-loop corrected propagator of magnetized fermions is determined, and the dispersion relations arising from the pole of this propagator are numerically solved. It turns out that in the lowest Landau level, where only one spin direction is allowed, the spectrum consists of one positively (negatively) charged fermionic mode with positive (negative) spin. In contrast, in higher Landau levels, as an indirect consequence of the double spin degeneracy of fermions, the spectrum consists of two massless collective... 

Using the standard Green-Kubo formalism, we determine the shear viscosity ? of a hot and dense Yukawa-Fermi gas. In particular, we study the effect of particle and plasmino excitations on thermal properties of the fermionic part of the shear viscosity, and explore the effects of thermal corrections to particle masses on bosonic and fermionic shear viscosities, ?b and η f . It turns out that the effects of plasminos on η f become negligible with increasing (decreasing) temperature (chemical potential)  

The differential multiplicity of dileptons in a hot and magnetized quark–gluon plasma, ΔB≡dNB/d4xd4q, is derived from first principles. The constant magnetic field B is assumed to be aligned in a fixed spatial direction. It is shown that the anisotropy induced by the B field is mainly reflected in the general structure of photon spectral density function. This is related to the imaginary part of the vacuum polarization tensor, Im[Πμν], which is derived in a first order perturbative approximation. As expected, the final analytical expression for ΔB includes a trace over the product of a photonic part, Im[Πμν], and a leptonic part, Lμν. It is shown that ΔB consists of two parts, ΔB ∥ and ΔB ⊥,... 

In order to gain deeper insight into the physics of the novel rotating solution of nonideal transverse magnetohydrodynamics (MHD), presented in one of our recent works, we replace the previously considered Maxwell theory with the CP violating Maxwell-Chern-Simons (MCS) theory. In this way, dissipationless chiral magnetic (CM) and anomalous Hall (AH) currents appear in the MCS equation of motion, that, together with equations of relativistic hydrodynamics, builds the set of constitutive equations of the nonideal transverse Chern-Simons magnetohydrodynamics (CSMHD). We are, in particular, interested in the effect of these currents on the evolution of electromagnetic fields in a uniformly and... 

In the first part of this work, a perturbative analysis up to one-loop order is carried out to determine the one-loop β-function of noncommutative U(1) gauge theory with matter fields in the adjoint representation. In the second part, the conformal anomaly of the same theory is calculated using Fujikawa's path integral method. The value of the one-loop β-function calculated in both methods coincides. As it turns out, noncommutative QED with matter fields in the adjoint representation is asymptotically free for the number of flavor degrees of freedom Nf < 3  

The noncommutative dipole QED is studied in detail for the matter fields in the adjoint representation. The axial anomaly of this theory is calculated in two and four dimensions using various regularization methods. The Ward-Takahashi identity is proved by making use of a nonperturbative path integral method. The one-loop β-function of the theory is calculated explicitly. It turns out that the value of the β-function depends on the direction of the dipole length L, which defines the noncommutativity. Finally using a semiclassical approximation a nonperturbative definition of the form factors is presented and the anomalous magnetic moment of this theory at one-loop order is computed